Current tank technologies use two main ammunition types for overcoming target armor. The first type is high explosive anti-tank projectiles equipped with an explosively driven warhead, which can penetrate steel armor plating to depths greater than seven times the diameter of the charge. The second type is armor-piercing fin stabilized discarding sabot projectiles equipped with kinetic energy penetrators. Kinetic energy penetrators are long-rod, armor-piercing projectiles that may be fired from modern high-velocity tank guns. These kinetic energy penetrators break through a target's armor by burrowing a cavity through its plating. Thus, armor-piercing fin stabilized discarding sabot ammunition does not contain explosives, but rather uses kinetic energy to damage the target. If the kinetic energy penetrator pierced through the armor, the combination of heat, spalling (particle spray), and the pressure wave generated during the penetration process can destroy the target.
Prior work in the field of the present disclosure has been directed toward replacing depleted uranium in kinetic energy penetrator applications. The density and “self-sharpening” behavior of depleted uranium, in particular, aid in the depth of penetration (and thus, damage) of a kinetic energy penetrator into a target.
Depleted uranium alloys, such as U-3/4Ti and U-8Mo alloys with high mass density (17-18 g/cm3) are highly desired as the penetrator core materials because of their outstanding combination of high strength, optimal and maintained ductility, as well as “self-sharpening” behavior. In the flow and shear failure behavior of depleted uranium alloy penetrators, early onset of adiabatic shear localization may occur at the head of the depleted uranium projectile, which helps discard any material build-up during penetration. Imaging of residual penetrators after perforating steel armor has shown that U-3/4Ti and U-8Mo alloys develop a chiseled and pointed nose, indicating early adiabatic shear failure and this material discard mechanism. However, depleted uranium penetrator materials, although mildly radioactive, derive their toxicity from the biochemical reactions within the human body after inhalation, ingestion, and/or other absorption methods. The uranium may then react to become toxic soluble salts and accumulate in the kidneys and other organs leading to failure or other health defects, such as the symptoms associated with Gulf War syndrome. Therefore, the use of depleted uranium has been restricted, and research for the past half-century has been focused on finding more environmentally friendly substitutes.
As part of this effort to replace depleted uranium alloys in kinetic energy penetrators, tungsten-based heavy alloys have emerged as attractive alternative candidate materials because of their unique combination of elevated temperature properties and high mass density (about 19.3 g/cm3). For example, conventional tungsten-based heavy alloys produced by liquid phase sintering—such as tungsten-nickel-iron (W—Ni—Fe) alloys—have been widely studied as depleted uranium alloy substitutes. However, conventional tungsten-based heavy alloy penetrators do not flow soften as quickly as depleted uranium alloy penetrators. Research in tungsten-based heavy alloy penetrators has shown that plastic localizations develop only after the tungsten-based heavy alloy has undergone very large plastic strains, which produces a large “mushroom” head and thus, reduces the full depth of penetration. This “mushroom” formation on the piercing head forms due to late shear localization and discard mechanisms.
In general, at the same firing velocity, depleted uranium alloy penetrators pierce deeper and generate smaller diameter penetration tunnels in a target as compared with conventional tungsten-based heavy alloy penetrators. Therefore, depleted uranium alloy penetrators have traditionally delivered better ballistic performance across multiple criteria.
Thus, to summarize, although other heavy metals and alloys have been investigated as potential replacements for depleted uranium in kinetic energy penetrators, the late or slow adiabatic shear localization of these replacement heavy metal alloys (such as tungsten-based heavy alloys) causes bulging deformations—which limit the penetration potential of the kinetic energy penetrator due to inefficient kinetic energy conservation during the tunneling process—and leads to failure of ballistic performance tests.